Lapping machine fixture



y 1963 s. A. BOETTCHER 3,090,169

LAPPING MACHINE FIXTURE Filed May 11, 1961 28heets-Sheet 1 INVENTOR.fiiyhenflzfioeiidzer J2 May 21, 1963 s. A. BOETTCHER 3,

LAPPING MACHINE FIXTURE Filed May 11, 1961 2 W fiV/VW/ T f 45 4446 w 24INVENTOR.

JivizenQBoeZZc/zex Sheets-Eben 2 This invention relates to lappingmachines and provides a fixture for lapping thin planar parts to anaccuracy of one ten-thousandth of an inch or less.

The fixture intervenes between the weight or pressure plate and the workpieces on the lapping surface within the truing retainer ring the basicidea being to allow lapping of the work pieces to finish thickness, andthen automatically discontinuing the lapping by removal of the downpressure, without stopping the machine.

The invention is illustrated in the accompanying drawings, in which:

FIGURE 1 is a cross-sectional view of the machine in general, takenapproximately on its vertical center line;

FIGURE 2 is a horizontal cross-sectional View, taken on the plane of theline 22 of FIGURE 1, looking downwardly, and on a larger scale, portionsbeing broken away;

FIGURE 3 is a vertical cross-sectional view, taken on the planes of thedot-and-dash line 33 of FIGURE 2, looking in the direction of thearrows; and

FIGURES 4 and 5 are two corresponding sectional views of a portion ofFIGURE 3, on a still larger scale, showing respectively, the positionsof the fixture before and after the lapping operation, the verticaldimension of the work piece being exaggerated for clarity.

Referring firstly to FIGURE 1:

The machine has a substantially cylindrical pedestal 11 supported by abase ring 12. The pedestal has an access door 13. A cylindrical collar14 is disposed within the upper end of pedestal 11, the same beingmounted 'by means of an inclined wall 15 forming a drip pan forreceiving abrasive and carrier mixture used in the lapping operationabove.

Mounted within the pedestal is a main drive motor 16 operativelyconnected by means of sheave Wheels 17 and 18 and a V-belt 19 with shaft20 of a conventional gear reducer unit 21, the output shaft 22 of whichcarries a hub member 23, upon which the horizontal circular plate ordisk 24, which provides the lapping surface 25, is mounted for rotation.This disk has a central well-bore 26, leaving an annular lapping area,and a plurality of radial slots 27 to lead the used abrasive and carriermixture to the drip pan 15.

Surrounding the lapping disk is a staging table 28 from which workpieces can be moved onto the lapping surface and to which they can bereturned when the lapping operation is completed.

Vertical channel columns 29, 29 are mounted in upright position atdiametrically opposite sides of the pedestal housing 11, joined at thetop by bridge member 30, which is provided with two intermediarytransverse arms 31, 31, having vertical bores for receiving verticallyadjustable spindles 32, two of which are shown. Each spindle has aknurled upper end 33 for manual grasping, and is held by a set screw 34.The lower end of each spindle is journaled in the center of a circularweight or pressure plate 35 and thus defines the axis of rotation ofsuch plate.

Each weight or pressure plate 35 fits, with slight clearance, within atruing-retainer ring 36 which rests on the lapping surface 25 of theplate or disk 24, and the weight or pressure plate rests upon thefixture to be described, which, in turn, rests upon the work pieces onthe lapping surface. The rings 36 function continuously to dress thelapping wheel for maintenance of its planar condition.

atent ce 3,090,169 Patented May 21, 1963 In the lower portion of thepedestal housing 11 there is provided a tank 37 for the abrasive andcarrier mixture, having a filling tube 37 and, within it, means 38,powered by motor 39, for agitating the said mixture and for circulatingit, by means of tubing 40 and 41, passing through one of the channelcolumns 29, to the level of the bleedotf spout 42, disposed inoverlapping relation to the plate or disk 24, for drop-by-drop feed ofthe mixture to the lapping surface 25.

The fixture of the present invention, indicated as a whole in FIGURE 1by the reference numeral 43, is there shown in elevation, disposedwithin the truing-retainer ring 36 between the weight plate 35 and thelapping disk 24 as above stated.

Reference is now made to FIGURES 2, 3, 4 and 5, illustrating the fixturein detail and on larger scales.

It comprises three elements, i.e. circular back plate 44, stop ring 45,and circular reference plate 46, together with retaining screw 47 andthree set screws 48.

The back plate 44 has a peripheral shoulder 49, which engages the top ofthe stop ring 45, tightly fitted to the reduced periphery of the plate,as shown. The reference plate 46 fits within the stop ring 45 withslight clearance. The work pieces, indicated at w, circular disks forinstance lie on the lapping surface 25, within the stop ring 45, and theunder surface of the reference plate engages the work pieces, the heavyblack lines above and below them indicating the films of lapping medium,i.e. the abrasive and carrier mixture above mentioned. The lower film oflapping medium of course extends under the stop ring and the truingretainer ring 36.

The stop ring 45 must not lap, and, accordingly, I make it of ceramicmaterial and select an aluminum oxide or garnet abrasive for the lappingmedium.

The height of the reference plate, relative to the bottom of the stopring determines the ultimate vertical dimension of the work pieces andis adjustable by means of the set screws 48, held as adjusted bytightening the retaining screw 47.

Work pieces which have been lapped on the one side in the usual manner,are inverted and so placed on the lapping surface 25 within the innerarea of the stop ring, and then the fixture 43 is placed upon them,followed by the Weight or pressure plate 35, a felt pad 51} betweenthem, if desired. A convenient method of loading the machine with thinwork pieces, is as follows: After the fixture has been adjusted for thedesired spacing of the under side of the reference plate 46 and thebottom of the stop ring 45, it may be inverted, a small amount oflapping medium spread on its exposed surface, and then laying the workpieces thereon, with light hand pressure, causing them to adhere; thefixture is then righted and placed on the lapping surface within thetruing-retaining ring, followed by the weight or pressure plate 35, afelt pad 50 intervening, if desired.

FIGURE 4 shows the parts at the start of the operation, and FIGURE 5shows them at the pre-determined completion of the operation. In thesefigures the vertical dimension of the work piece has been exaggeratedfor purposes of clarity.

The fixture provides means for determining in advance the verticaldimension of the work pieces with the utmost accuracy, and when theselected dimension has been attained the lapping ceases automatically,and continued operation of the machine is without effect.

I claim:

1. In a lapping machine fixture for predetermining the extent of lappingwork pieces positioned on a rotating lapping disc within a truing andretaining ring thereon, a plate for resting on said work pieces, asecond plate parallel thereto and adjustably distanced therefrom, andmeans carried by said second plate for engaging the lapping disk toarrest the downward movement of said plates.

2. In a lapping machine fixture for predetermining the extent'of lappingwork pieces positioned on a rotating lapping disc within a truing andretaining ring thereon, a plate for resting on said Work pieces, asecond plate parallel thereto and adjustably distance-d therefrom, and aring carried by said second plate surrounding said firstnamed plate forengaging the lapping disk to arrest the downward movement of saidplates.

3. In a lapping machine fixture for predetermining the extent of lappingwork pieces positioned on a rotating lapping disc within a truing andretaining ring thereon, a plate for resting on said work pieces, asecond plate parallel thereto, set screws in one of said plates forengaging the other plate to adjust the distance between them, means forsecuring said plates together in adjusted position, and a ring carriedby said second plate for engaging the lapping disk to arrest thedownward movement of said plates.

4. In a lapping machine fixed for predetermining the extent of lappingwork pieces positioned on a rotating lapping disc within a timing andretaining ring thereon, a plate for resting on said work pieces, asecond plate parallel thereto and adjustably distanced therefrom, and aceramic ring carried by said second plate surrounding said first-namedplate for engaging the lapping disk to arrest the downward movement ofsaid plates.

5. In a lapping machine fixture for predetermining the extent of lappingwork pieces positioned on a rotating lapping disc within a truing. andretaining ring thereon, a first horizontal plate for resting on saidwork pieces, a second horizontal plate parallel thereto and adjustablydistanced thereabove, said second plate having an annular reducedperiphery defining a peripheral shoulder, an annular ring at its upperend forcibly fitted to said redumd periphery and seated against saidshoulder in said second plate, said ring having an inner diametersubstantially conforming to the outer diameter of said first plate, andsaid ring extending axially downwardly beyond the plane of the lowerface of said first plate for engaging the lapping disc to arrest thedownward movement of said plates.

6. The combination of claim 5 characterized by the provision of setscrews in one of said plates for engaging the other plate to adjust thedistance between them, and

means for securing said plates together in adjusted 1 position.

References Cited in the file of this patent UNlTE-D STATES PATENTS2,565,590 Bullard Aug. 28, 1951 2,722,089 Boettcher Nov. 1, 19552,842,906 Carter et al. July 15, 1958 2,967,380 =Damgaard Ian. 10, 19612,971,298 Garthwaite et al. Feb. 14, 1961 2,979,868 Emeis Apr. 18, .19612,983,086 La Chapelle May 9, 1961

1. IN A LAPPING MACHINE FIXTURE FOR PREDETERMINING THE EXTENT OF LAPPINGWORK PIECES POSITIONED ON A ROTATING LAPPING DISC WITHIN A TRUING ANDRETAINING RING THEREON, A PLATE FOR RESTING ON SAID WORK PIECES, ASECOND PLATE PARALLEL THERETO AND ADJUSTABLY DISTANCED THEREFROM, ANDMEANS CARRIED BY SAID SECOND PLATE FOR ENGAGING THE LAPPING DISK TOARREST THE DOWNWARD MOVEMENT OF SAID PLATES.